Method for the percutaneous creation of an arteriovenous fistula (avf)

ABSTRACT

This document relates to the apparatus and methods used in the minimally invasive creation of arteriovenous fistula (AVF). In particular, the invention relates to the creation of an AVF using catheters and an alignment methodology that is based upon detection of asymmetric electric fields. The invention finds particular application in vascular access (VA) in the hemodialysis (HD) population.

This application is a continuation of PCT/US2016/021782, filed Mar. 10,2016; which claims priority of GB1504060.3, filed Mar. 10, 2015;GB1511692.4, filed Jul. 3, 2015; and U.S. Provisional Application No.62/209,153, filed Aug. 24, 2015. The contents of the above-identifiedapplications are incorporated herein by reference in their entirety.

FIELD

The invention relates to the apparatus and methods used in the minimallyinvasive creation of arteriovenous fistula (AVF). In particular, theinvention relates to the creation of an AVF using catheters andalignment methodology. The invention finds particular application invascular access (VA) in the hemodialysis (HD) population.

BACKGROUND

More than half a million patients in the US and Western Europe whosekidneys are failing and need to undergo hemodialysis face a significantrisk. This risk is due to the limitations and performance issues ofcurrent methods for a dialysis machine to connect to a patient'scirculatory system known as a vascular access (VA) site. Achievinglong-term vascular access which remains patent and infection free isvery difficult. (See Leermakers et al. (2013); US Dept. Health and HumanServices Report (2014); and Al-Jaishi et al. (2014)).

Vascular access can be achieved in one of three ways: arteriovenousprosthetic grafts (AVG), tunneled central vein catheter, or nativearteriovenous fistula (AVF). The main function of both the AVF and theAVG is to create a “short circuit” in the peripheral vasculature bydirectly connecting high-pressure arterial flow and low-pressure venousflow. This results in a greatly increased flow rate, which is necessaryfor dialysis, in the graft or the vein. The latter also enlarges andarterializes making it easier to cannulate.

Currently a patient requires open surgery with local or generalanesthesia to receive an AVF. Once the AVF has been created one needs towait until it matures and is ready to be used for hemodialysis (HD).VA's can fail due to a variety of reasons including thrombosis,stenosis, infection, or neointimal hyperplasia. Overall, there is a needfor a VA which is easy to implant, matures quickly and has a highpatency rate.

Minimally invasive surgery is a common method to perform a variety ofcardiovascular procedures. It is typically performed using cathetersthat are inserted into various lumens within the body through smallincisions in the skin. A percutaneous approach to AVF creation hasseveral clinical benefits including simplifying the procedure andreducing surgical trauma to the vessels which has a negative effect onpatency.

Several technologies have been developed with the purpose of creating anarteriovenous fistula percutaneously however none have been approved forclinical use. All of the following technologies employ one or twocatheters in order to create an anastomosis between two adjoining bloodvessels. U.S. Pat. No. 8,523,800 describes technology for forming afistula with the aim of treating COPD patients and those withhypertension. U.S. Pat. No. 5,830,222 and WO2006/027599 describetechnology for percutaneously connecting two vessels to divert arterialblood to the venous system, and U.S. Pat. No. 6,475,226 describes analternative to coronary bypass surgery. US2013/0281998 andUS2012/0302935 describe technologies for percutaneously creatingfistulas for dialysis use.

There are several suitable anatomical locations for the vascularanastomosis which allow for the formation of a vascular access sitesuitable for haemodialysis. The most commonly used include in the radialartery and cephalic vein at the wrist level, the brachial artery andcephalic vein at the antecubital fossa, and the brachial artery andbasilic vein in the upper arm. Less commonly a fistula can be created inthe upper leg between the saphenous vein and femoral artery.

There are two main approaches to using intravascular catheters forcreating the anastomosis; one technique involves placing a tube or stentgraft between the two vessels in order to form the connection, the othercreates a hole directly between the two vessels where they are closetogether. Implementing either technique requires an active means toalign the two catheters, as fluoroscopy is not adequate for the angularalignment. Accurate alignment is more important in the first case whenthe ratio of the vessel separation to the vessel diameters increases.

Several different modalities for radial alignment have been presented inthe literature and typically include a transmit catheter sending asignal toward a receive catheter which measures the magnitude of thesignal and relays that information as an indication of alignment.Different types of signals include ultrasound (see, for example,WO2006/027599, US2004/0133225), light (see, for example, U.S. Pat. No.6,475,226), and inductive fields (see, for example, EP1377335). However,a drawback of such methods is that they require relatively complexmechanical or electronic transducers, to generate and receive thesignals, which can be difficult and expensive to manufacture and limitthe size of the catheters, in particular their suitability for use insmaller diameter vessels.

SUMMARY

The present invention provides methods and apparatus for improving theperformance of a percutaneous surgical AVF procedure over the prior artmethods using an alignment method based in some embodiments upondetection of a directional signal such as, but not limited to, electricfield orientation. This invention allows for the creation of apercutaneous AVF via a system and apparatus that comprises two catheterswhich are smaller, cheaper to produce, and easier to operate than thoseprovided in the prior art. In particular, the method described appliesto the creation of an AVF for use as VA in hemodialysis patients.

Accordingly, in a first aspect the invention provides a method forimproving venous access in a patient in need thereof by creating afistula between a first vessel and a second vessel, the methodcomprising the steps of:

-   -   a) inserting, via a percutaneous route, a first device into the        first vessel, wherein the first device comprises a catheter that        comprises a directional signal source, and wherein the first        device further comprises a penetrating element that is capable        of being advanced radially outwardly from the first device, the        direction of advancement of the penetrating element being        aligned to a directional signal produced by the directional        signal source;    -   b) inserting, via a percutaneous route, a second device into the        second vessel, wherein the second device comprises a sensor,        wherein the sensor is capable of detecting a directional signal;    -   c) generating a directional signal and aligning the first and        second devices relative to each other such that penetrating        element is advanced radially from the first vessel towards the        second vessel, thereby forming a channel enabling fluid        communication between the first and second vessels; and    -   d) enlarging the channel to form a fistula.

A second aspect of the invention provides for a method of connecting twoadjacent vessels within the body of a patient, said method comprisingthe steps of:

-   -   a) introducing a first source device into a first vessel, the        first device comprising at least one signal electrode for        generating an asymmetric electric field;    -   b) introducing a second sensing device into a second vessel, the        second device comprising at least one detector for detecting the        asymmetric electric field;    -   c) aligning the first and second device relative to each other        based on the electric field generated by the first device that        is detected by the detector on the second device;    -   d) forming a conduit between the first vessel and the second        vessel; and    -   e) removing the first and second devices to leave the first and        second vessels connected via the conduit.

A third aspect of the invention provides a system for connecting twovessels within the body of a patient, the system comprising:

-   -   a) a first source device that is located in a first vessel, the        first device comprising at least one signal electrode for        generating an asymmetric electric field;    -   b) a second device located in a second vessel adjacent to the        first vessel, the second device comprising at least one detector        for detecting the asymmetric electric field; and    -   c) connection apparatus for connecting the two vessels        wherein, the connection is directed by aligning the first device        with the second device via the asymmetric electric field        generated by the first device being detected by the second        device, and delivering the connection apparatus along the        direction indicated by the alignment.

Optionally the connection apparatus comprises the first source device.Suitably, the at least one signal electrode is located on the connectionapparatus. Alternatively, either the first or the second devicescomprise the connection apparatus. Typically, the first and/or seconddevices comprise catheters. Suitably, the first and/or second devicescomprise guidewires. In embodiments of the invention where the firstdevice comprises the connection apparatus, the first device is alsoreferred to herein as the ‘launching device’. Likewise, where the seconddevice does not comprise the connection means it is, thus, also referredto herein as the ‘target device’.

A fourth aspect the invention provides a system for connecting twovessels within the body of a patient, the system comprising:

-   -   a) a launching device suitable for location within a first        vessel, the launching device comprising        -   (i) an elongate outer sheath with a distal end and a            proximal end, the outer sheath defining and enclosing an            interior lumen;        -   (ii) a signal transducer located at the distal end of the            outer sheath, the signal transducer being arranged so as to            generate an asymmetric electric field; and        -   (iii) a traversing member for traversing the tissue            intervening the first and second vessels, the traversing            member being movable between a retracted position within the            lumen at the distal end of the outer sheath of the launching            device, and a deployed position extending outside of the            outer sheath of the launching device;            and    -   b) a target device suitable for location within a second vessel,        the target device comprising        -   (i) an elongate outer sheath with a distal end and a            proximal end, the outer sheath defining and enclosing an            interior lumen; and        -   (ii) a detector located at the distal end of the outer            sheath;            wherein, in use, the signal transducer on the launching            device generates an asymmetric electric field that is            capable of being detected by the detector on the target            device, and when the signal is detected by the detector on            the target device it is determined that the devices are            located in the correct alignment within their respective            vessels such that the traversing member can be deployed from            its retracted position within the launching device to            traverse the tissue intervening the first and second vessels            and form a connection between the first vessel and the            second vessel.

A fifth aspect of the invention provides a system for traversing tissueintervening first and second body cavities comprising:

-   -   a) a first source device that is located in a first body cavity,        the first device comprising at least one signal electrode for        generating an asymmetric electric field;    -   b) a second device located in a second vessel adjacent to the        first body cavity, the second device comprising a detector for        detecting the asymmetric electric field generated by the first        source device;    -   c) connection apparatus for connecting the first body cavity and        the second body cavity; and    -   d) an electronic alignment monitor unit that is in communication        with the first and second devices that is capable of generating        the asymmetric electric field in the source device, and detected        signal in the target device, and provide a visual or audible        display to indicate alignment to the user.        wherein, the connection is directed by aligning the first device        with the second device via the asymmetric electric field        generated by the first device being detected by the second        device, and delivering the connection apparatus along the        direction indicated by the alignment.

Optionally, the electronic alignment monitor unit is comprised within ahandle that connects to the first device via rotational connectors(commutators). Typically, the connection acts as an arterio-venousfistula to provide vascular access for dialysis. Suitably, theconnection creates a radial cephalic fistula, a brachial cephalicfistula, a brachial basilic fistula or a basilic basilic fistula.

A sixth aspect of the invention provides for a percutaneous surgicalcatheter device comprising:

-   -   (a) an elongate body having distal and proximal ends, the body        comprising a hollow sheath, which sheath defines a lumen that        extends along at least a substantial portion of the body;    -   (b) a signal transducer located within the distal end of the        elongate body, wherein the signal transducer is arranged to        generate an asymmetrical electric field;    -   (c) a penetrating member that is housed slideably within the        lumen and is capable of extension out of the distal end of the        elongate body;        wherein the direction of extension of the penetrating member is        aligned with the asymmetrical electric field.

A seventh aspect of the invention provides for a percutaneous surgicalcatheter device comprising:

-   -   (a) an elongate body having distal and proximal ends, the body        comprising a hollow sheath, which sheath defines a lumen that        extends along at least a substantial portion of the body;    -   (b) a penetrating member that is housed slideably within the        lumen and is capable of extension out of the distal end of the        elongate body;    -   (c) a signal transducer located within the distal end of the        penetrating member, wherein the signal transducer is arranged to        generate an asymmetrical electric field;        wherein the direction of extension of the penetrating member is        aligned with the asymmetrical electric field.

In an eighth aspect of the invention provides for a penetrating memberfor use in a percutaneous surgical catheter device, the penetratingmember having a proximal and a distal end, wherein at or near the distalend of the penetrating member is located a signal transducer, whereinthe signal transducer is arranged to generate an asymmetrical electricfield.

In a specific embodiment of the seventh and eighth aspect of theinvention, the elongate body comprises an aperture in the side wall inor near to the distal end, thereby allowing extension of the penetratingmember in a direction that is substantially radial relative to thelongitudinal axis of the elongate body. Suitably, the signal transducercomprises at least two electrodes and is capable of generating anelectric field, or optionally at least four signal electrodes.Optionally, the electrodes are switchable to produce fields of varyingangular dependence. In a specific embodiment, the electrodes areswitchable to produce multipolar (e.g. dipole and/or quadrupole) fields.

Suitably, the signals from transmitted fields of varying angulardependence are combined using an algorithm to produce a composite signalwith enhanced angular dependence. In a specific embodiment, thepercutaneous surgical catheter device according to the present inventionfurther comprises one or more ring electrodes positioned proximal and/ordistal to the signal electrodes to permit longitudinal alignment of thesystem.

Optionally, the penetrating member comprises a hollow needle. Suitably,the crossing needle is formed of shape memory alloy—such as nitinol—orstainless steel or titanium. Alternatively the penetrating member maycomprise a flexible guidewire with an optional sharpened tip. In aspecific embodiment, the crossing needle is heated so that it bends aspart of its deployment. Alternatively, the hollow needle is formed ofone or more sections arranged concentrically within the inner lumen in atelescopic manner.

DRAWINGS

The invention is further illustrated by reference to the accompanyingdrawings in which:

FIGS. 1a and 1b represent an embodiment of the apparatus of theinvention comprising an arterial (source) catheter (FIG. 1a ), a venous(sensing) catheter (FIG. 1b ), and a handle and a user interface of thedevice.

FIG. 2a is a more detailed representation of the source catheteraccording to an embodiment of the present invention.

FIG. 2b is a cross sectional representation of the source catheter ofFIG. 2a along the line of BB.

FIG. 2c is an expanded view of the distal end of the source catheterwithin the circle E in FIG. 2 a.

FIG. 2d is a sectional view of an embodiment of a penetration member ofthe source catheter comprising two hollow pre-curved needles.

FIG. 3a is a representation of an embodiment of the apparatus of theinvention with signal source electrodes arranged on the penetrationmember, and the sensing catheter.

FIG. 3b is a representation of an embodiment of the apparatus of theinvention with two pairs of signal source electrodes arranged on thepenetration member in a diametrically opposed fashion, and the sensingcatheter

FIG. 3c shows a cross-sectional view of the penetrating member shown inFIG. 3 b.

FIG. 3d is a representation of an embodiment of the apparatus of theinvention with a single source electrode forming the tip of thepenetrating member

FIG. 3e is a representation of an embodiment of the apparatus of theinvention with a single source electrode comprising of the entire lengthof the penetrating member.

FIG. 4a is a representation of a specific embodiment of the sensingcatheter according to an embodiment of the present invention.

FIG. 4b is a cross sectional representation of the sensing catheter ofFIG. 4a along the line of AA.

FIGS. 5a-c are detailed representations of a specific embodiment of thesystem handle and user interface.

FIG. 6a is a diagram indicating the typical measured field strengthversus the rotation of the source catheter relative to the sensingcatheter.

FIG. 6b is a diagram showing the measured field strength vs the rotationfor a two element and a four element electrode, and how they combined togive a narrower peak.

FIG. 6c is a graph showing signal measured from longitudinal alignmentelectrodes.

FIG. 7 is a block diagram representation of a specific embodiment of theoverall electronic control system for the invention.

FIGS. 8a to f is a chronological step-wise representation of theclinical procedure for using the device to connect two adjoining bodyvessels—in this embodiment an artery and a vein—with a covered stentgraft.

DETAILED DESCRIPTION

All references cited herein are incorporated by reference in theirentirety. Unless otherwise defined, all technical and scientific termsused herein have the same meaning as commonly understood by one ofordinary skill in the art to which this invention belongs.

The invention provides for apparatus in the form of medical devices eachcomprising an elongated shaft assembly, typically in the form of acatheter that comprises functional elements at the distal portion and auser or operator interface at the proximal terminus. The user interfacemay comprise a handle, handle assembly or hub.

Prior to setting forth the invention, a number of definitions areprovided that will assist in the understanding of the invention.

As used herein, the term “comprising” means any of the recited elementsare necessarily included and other elements may optionally be includedas well. “Consisting essentially of” means any recited elements arenecessarily included, elements that would materially affect the basicand novel characteristics of the listed elements are excluded, and otherelements may optionally be included. “Consisting of” means that allelements other than those listed are excluded. Embodiments defined byeach of these terms are within the scope of this invention.

As used herein the terms distal and proximal are used to refer toorientation along the longitudinal axis of the apparatus. Since thedevices of the invention are elongate in nature and conform to a singledimension, in use the distal direction refers to the end of the devicefurthest away from the operator and the proximal direction the end ofthe device closest to the operator. It should be noted that the termproximal should not be confused with the term ‘proximate’, which adoptsits conventional meaning of ‘near to’.

In its broadest configuration the apparatus of the invention comprisesan elongate shaft assembly which may engage with or attach to a handleassembly. The elongate shaft is suitably configured for percutaneoususe, such as via the intravascular, intra-venous and intra-arterialmodes; that involves introduction into a hollow anatomical vessel withinthe body of a subject animal or patient. The handle assembly remainsoutside—i.e. external to—the body of the subject. In a specificembodiment of the invention the elongate shaft comprises or consists ofa catheter, suitably comprising a tube portion that may define one ormore lumens located coaxially within the shaft. The catheter may beadapted for use with an associated guide wire in conventionover-the-wire (OTVV) or monorail configurations. In embodiments wherethe catheter is adapted for use with a guide wire, the catheter mayfurther comprise an additional lumen that is adapted to accommodate aguide wire. Any such guide wire may be pre-located within the subject inorder to facilitate placement of the device when in use.

The device of the present invention is suitable for intravascular use.In embodiments of the invention the device may be used within thecentral vasculature such as the coronary artery and vein as well as inperipheral vasculature such as the blood vessels of the limbs, the headand neck, the groin, or anywhere suitable for the creation of anarterio-venous fistula.

The AVF Surgical Device

According to a specific embodiment, the apparatus of the currentinvention comprises three main components: a source catheter 10, asensing catheter 100, and an electronic alignment monitor system 200.According to one embodiment of the invention the source catheter 10 maybe located within an artery and the sensing catheter 100 may be locatedwithin an adjacent vein, or vice versa.

According to one embodiment of the invention the term “catheter” refersto a device that comprises an elongated shaft. The shaft is typically isprovided with a central lumen that extends along its entire length. Theelongate shaft of embodiments of the invention are suitably constructedas catheters in a variety of sizes typically ranging from about 0.15 mmup to about 4 mm in diameter (corresponds to French sizes 0.5 to 12).The elongate shaft is suitably constructed from a polymeric materialsuch as a silicone rubber or a polymer including thermoplasticelastomer, PEEK, polyimide, high density polyethylene (HDPE), Pebax,and/or nylon; or composites thereof. All or a portion of the shaft mayalso comprise a low friction or lubricious coating that may, forexample, include a fluoropolymer such as a PTFE or parylene. All or aportion of the shaft may also be reinforced using various arrangement ofmetallic filaments. All or a portion of the shaft may also be replacedby laser cut metallic tubing such as nickel titanium alloy, stainlesssteel, or other biocompatible metal alloys.

A central lumen 38 provides a conduit which may allow engagement with apre-located guide wire. The central lumen 38 may extend entirely alongthe shaft such that the within or adjacent to the distal terminus thereis comprised an aperture allowing fluid communication between thecentral lumen and the hollow anatomical structure within which the shaftis located. In an embodiment of the invention, the central lumen isformed from a polymer liner that sits coaxially within the elongateshaft. Suitably the polymer liner is comprised of a material such as afluoropolymer, for example PTFE. In an embodiment of the invention thedistal portion, at least, of the polymer liner may be linked orotherwise fixed to the distal part of the elongate shaft and the mainportion of the polymer liner is allowed to move freely within and withrespect to the elongate shaft. Embodiments of the invention permit forlocation of the central lumen centrally within the body of the elongateshaft or at a position that is radially offset from the centrallongitudinal axis

FIG. 1a shows an embodiment of a source catheter 10 according to thepresent invention. The source catheter 10 comprises an elongate body 12having a proximal and distal end. Toward the proximal end of the body 12is positioned a first Luer connector 14 in communication with the body12; and a second Luer connector 16 in communication with the lumen ofthe penetrating member 20.

The source catheter 10 further comprises a guide wire 18 that isoperable between a retracted position wherein the guide wire 18 isretained within the lumen, and an extended position wherein the guidewire 18 extends outwardly from the distal end of the lumen, and apenetrating member 20. The guide wire 18 runs co-axially within thepenetrating member 20 for the entire length of the catheter 10. Thepenetrating member 20 is constrained inside the catheter 10 to lie alongthe axis of the catheter 10. The penetrating member 20 has a pre-formedcurve at its distal end, so that when it exits the catheter 10 it adoptsa shape that curves in a radial direction with respect to the axis ofthe catheter 10. In the embodiment shown in FIG. 1a , the penetratingmember 20 is ejected through an opening or aperture 19 in the side wallof the catheter 10. The aperture 19 may be covered with a sliding cover21 such as a tube or sleeve (not shown) that can be withdrawn when thepenetrating member 20 is ejected. Furthermore, only when the guide wire18 is in the retracted position can the penetrating member 20 be ejectedfrom the catheter 10.

The penetrating member 20 may be a retractable hollow needle or styletformed from a suitable material including polyether ether ketone (PEEK),carbon fibre loaded liquid crystalline polymer, tungsten carbidepolyimide, stainless steel, gold, platinum, shape memory alloy(including NiTinol) or other suitable surgically compatible metalalloys. Typically, the penetrating member is formed from a radiopaquematerial so as to facilitate visualisation during surgical procedureswhen using X-ray guidance. The penetrating member 20 may furthercomprise one or more echogenic surfaces to further facilitate use withultrasound visualisation (e.g. IVUS, phased array) technologies. Thepenetrating member 20 is provided with a sharp tip at its distal end,which is used to puncture and penetrate tissue at the site of treatment.The lumen of the penetrating member 20 allows the delivery of a standardguide wire 18 from one vessel to another. The lumen of the penetratingmember also allows for administration of substances, including andpharmaceutical compositions and contrast medium, to the site oftreatment through the lumen of the penetrating member 20 if required.The lumen of the penetrating member 20 may also be used as an aspirationchannel to extract fluids from the site of treatment and/or to take atissue biopsy.

Toward the distal end of the body 12 there are positioned a pair ofelectrodes 22, 24 spatially separated around the circumference of thebody 12 such that they are substantially diametrically opposed. In oneembodiment of the invention, the pair of electrodes 22, 24 are arrangedalong an axis that is substantially aligned with the direction ofdeployment of the penetrating member when it is extended outwardly fromthe source catheter. As best seen in FIG. 2a , electrode wires 26, 28(not shown) extend proximally from the electrodes along the lumen untilthey connect with pads 34 and 36 on the rigid clip-on section 32.

In the embodiment of the invention shown in FIGS. 1a to 1c , a handle 30provides a first user interface with the catheter 10. The handle 30 isremovably attached to the body 12 via the rigid clip-on section. Thehandle 30 is arranged on the body 12 so as not to interfere withinsertion of the catheter 10 into the body, suitably the handle 30 ispositioned toward the proximal end of the body 12.

FIG. 1b shows an embodiment of a sensing catheter 100 according to thepresent invention. The sensing catheter 100 comprises an elongate lumen102 having a proximal and distal end. Toward the proximal end of thelumen 102 is positioned a Luer connector 104.

The sensing catheter 100 comprises a hollow guide wire 106 and two ringelectrodes 108, 110. Electrode wires 112, 114, each of which isconnected to a respective ring electrode, extend proximally in theinterior of the lumen 102 and exit the lumen at the proximal end throughthe Luer connector 104.

Having described the main features of the apparatus comprising thesource catheter 10 and sensing catheter 100, a detailed description ofthe features presented will now be provided with reference to FIGS.2a-d, 3a-b, and 4a -c.

As shown in FIG. 2a , the source catheter 10 comprises several elongatedtubes that are coaxially aligned and have overall a proximal and distalend. FIGS. 2a-c show the features of the source catheter 10 in moredetail.

FIG. 2a shows the source catheter 10 in side view with the handle 30removed. On the body of the catheter 10 there is a rigid clip on section32 of a larger diameter than the body 12 which comprises two ringelectrodes 34, 36. This section is formed so as to mate with the handle30 and allow for free rotation of the handle through a 360 degreeelectrical connection.

The first Luer connector 14 allows for the manipulation of sourcecatheter 10 and the second Luer connector 16 allows for the manipulationof a penetrating member 20 such as a needle while stopping blood fromexiting. The penetrating member 20 and Luer connector 16 also allow fora syringe to be connected and facilitate the insertion of therapeuticagents, for example, contrast medium.

In one embodiment of the catheter 10 the two electrodes 22, 24 arediametrically opposed each occupying less than half of the circumferenceof the body 12. In an embodiment of the invention, one electrode 22serves as the positive electrode, and the second 24 serves as a negativeelectrode, thereby forming a dipole configuration. Several otherarrangements are also possible, such as an evenly spaced array of morethan two electrodes arranged around the circumference of the body 12,embodiments of this type would suitably include quadrupole or octupoleconfigurations of electrodes. The electrodes 22, 24 are located distallyto the penetrating member 20 along the body of the source catheter 10 inorder to be aligned with the end of the penetrating member 20 whenejected. This ensures that point which the penetrating member 20punctures into the vein corresponds to and is aligned with the positionof peak field strength generated by the electrodes. In an alternativeembodiment the electrodes 22, 24 can be located proximal to thepenetrating member 20.

A cross section along BB of a source catheter 10 according to anembodiment of the invention is shown in FIG. 2b . The catheter 10comprises a coaxial arrangement of an outer sheath 35 that surrounds andthereby defines an inner lumen 38. Located within the lumen 38 is aninner sheath 37. The inner sheath 37 is connected to the outer sheath 35using adhesive throughout the whole length of the catheter 10. Theelectrode wires 26, 28 are also located within the lumen 38 and pass inan axial direction along the lumen 38 to the proximal end of the device.The inner sheath 37 and outer sheath 35 may be formed of any materialthat can prevent the ingress of water and other bodily fluids such thatthe lumen 38 is substantially waterproof. This protects any electricalsignal passing through the electrode wires 26, 28 from shorting. In analternative embodiment, the outer sheath 35 and inner sheath 37 arereplaced by one sheath. In this embodiment, the electrode wires areembedded directly within the single sheath.

The inner sheath 37, when present, defines an inner lumen within whichis positioned the penetrating member 20, such as a needle, andoptionally a guide wire 18. In order to facilitate use of the catheter10, the guide wire 18 may be located coaxially within the hollow core ofthe penetrating member 20. In this way the penetrating member 20 isprevented from extending outside the body 12 while the guide wire 18 isin position. Only when the catheter 10 is aligned and the guide wire 18is removed can the penetrating member 20 be advanced from the opening 19in the side wall of the catheter body 12. This embodiment of theinvention avoids the need for a preformed needle to be inserted duringthe procedure and risk disrupting the alignment. This arrangement alsoremoves the need for a separate guide wire lumen. Alternatively, if theoperator prefers to use a guide wire of greater diameter than thatpermitted by the size of the needle—particularly in smaller devices thatare intended for paediatric use—the guide wire 18 may sit within theinner lumen and be removed and replaced with the penetrating member 20at the appropriate point during the procedure. Furthermore, in analternative embodiment the guide wire 18 may be arranged in an externalmonorail configuration and sliding cover or sheath 21 may be used toprevent the penetrating member 20 from exiting the lumen.

Electrode wires 26, 28 provide electrical connection from each electrode22, 24 to a respective ring electrodes 34, 36 in the rigid clip onsection 32 positioned towards the proximal end of the catheter 10. Inthis embodiment the ring electrodes 34, 36 form a convenient rotaryconnection with the handle 30 when attached to the rigid clip on section32 thereby preserving electrical connection between the handle 30 andthe source catheter 10 through any degree of rotation about the axis ofthe catheter 10. Other embodiments using an electrical plug orconventional hub are also suitable.

An expanded view of the distal end of the source catheter 10 is shown inFIG. 2c . The typical spatial arrangement of the two electrodes 22, 24is shown. In this embodiment, the electrodes 22, 24 are aligned anddiametrically opposed on either side of the catheter body 12. In anotherembodiment the electrode, or each pair of electrodes, are diametricallyopposed but not aligned, with one electrode axially offset from theother electrode along the body 12. Through the opening 19 thearrangement of the guide wire 18 passing through the penetrating member20 is also visible demonstrating how the guide wire is able to lock thepenetrating member 20 in place prior to withdrawal of the guide wire 18and deployment of the penetrating member 20.

In an embodiment of the source catheter 10 (not shown) the penetratingmember 20 may be a straight tube made of a shape memory alloy, with aninsulated conducting wire installed into the lumen. The distal end ofthe wire will have the insulation removed, so that an electrical circuitis formed from the proximal end of the wire to its distal end, via anelectrical contact with the distal end of the penetrating member, andthen from the distal end of the penetrating member to its proximal end.If electrical contact is then made to the proximal end of both thetubular penetrating member and the central wire a pulsed electricalcurrent is passed through the circuit. This will heat the penetratingmember above its transition temperature and deform the member to adopt apreset curved shape that will then cross from one vessel to another.Changing the mark-space ratio of the current waveform can generate aproportional control of the deformation.

As shown in FIG. 2d , the penetrating member 20 of another embodiment ofthe source catheter 10 is shown consisting of two hollow needlesarranged concentrically within the inner lumen. Each needle has apre-defined curvature. The needles are deployed one after the other in atelescopic manner, so that the penetrating member 20 has an increasedlength and angular curvature.

In an embodiment of the invention one or more further electrodes aremounted on the distal end of the penetrating member 20. In thisembodiment the entire penetrating member is insulated except for asection of the distal end that forms an electrical connection to thepenetrating member 20 at its proximal end. The one or more furtherelectrodes are not activated when the penetrating member is retractedand only become active when the penetrating member has exited thecatheter. Once activated, these one or more further electrodes form anasymmetric electric field. This allows for fine adjustment of thealignment of the penetrating member as it is crossing from the artery tothe vein to ensure that it remains on target. Furthermore, in thisconfiguration, the sensing catheter 100 will detect when the penetratingmember has successfully penetrated into the vein based on severaldifferent measurements including amplitude and conductance.

In FIG. 3a a penetrating member 20 is shown that has a positive ringelectrode 39 and a negative ring electrode 41 on its distal tip. Theelectrodes 39, 41 together generate a directional electric field. Thesensing electrodes 108, 110 on the sensing catheter 100 measures thedipole electric field created by the two source electrodes 39, 41. Asthe penetrating member 20 approaches the sensing catheter 100 themeasured signal will reach a maximum when the tip of the penetratingmember 20 is nearest the sensing electrode 100. If the penetratingmember 20 advances beyond (i.e. overshoots) the sensing catheter 100 thesignal will start to decrease. As an alternative, the sensing electrodes108, 110 can be located on the penetrating member 20 and the sourceelectrodes 39, 41 are on the sensing catheter 100. This functionalitycan be accomplished electronically or using software to configure theapparatus accordingly.

FIG. 3b shows an alternative embodiment of the penetrating member 20having two pairs of source electrodes 39, 41 on its distal end. Eachpair of source electrodes 39, 41 are arranged in a diametrically opposedfashion on a circumference of the penetrating member 20; the first pairof electrodes 39, 41 angularly displaced by approximately 90° from theother pair of electrodes. This is best shown in FIG. 3c which is across-sectional view of the penetration member 20 at the position of theelectrode pairs.

Each pair of electrodes creates a dipole electric field with a zerovalue along a plane that lies equidistant between them when theelectrodes are activated. In this arrangement the signal measured by theelectrodes 108, 110 on the sensing catheter 100 will vary with movementof the penetrating member 20 in the x-y plane (i.e. along or across thelongitudinal axis L of the sensing catheter 100; as shown in FIG. 3c ).A measured value of OV when both pairs of electrodes are activeindicates that the penetrating member 20 is aligned with the positivesensing catheter electrode 108. A value greater than OV indicates adegree of misalignment. The amplitude of signal is indicative ofalignment with values closer to null (OV) indicating greater alignment.

This embodiment need not be limited to having two pairs of electrodes.Similar functionality may be achieved with three or more pairs ofelectrodes, for example, 4 pairs or 8 pairs (i.e. quadropole oroctopole), or more pairs of electrodes on the penetration member 20.

FIG. 3d shows another embodiment of a penetrating member 20 having oneor more electrodes. In this embodiment, the penetrating member 20 has asingle ring source electrode 45 that forms the tip of the penetratingmember 20. When the penetrating member is formed of a conductingmaterial, such as metal, this configuration requires insulating material47 to separate the electrode 45 that forms the tip of the penetrationmember 20 and the remainder of the penetration member 20. A wire 49connects the electrode 45 to a power source. In use, current is appliedto the source electrode 45 and a voltage is measured on the sensingelectrode 108 relative to the ground signal measured from the groundingelectrode 110 on the sensing catheter 100. In an alternative embodimentthe electrode 45 acts as voltage source and the current is measured atelectrode 108. The current or voltage measured by the electrode 108 onthe sensing catheter 100 will increase when the tip of the penetratingmember 20 is nearest the sensing electrode 108 and will be at a maximumif the penetrating member 20 contacts the sensing electrode 108. A highor maximum signal may be used to indicate that the penetrating memberhas successfully entered the vessel. FIG. 3e shows an alternativeembodiment where the entire penetrating member 20 acts as the sourceelectrode 45 and functions as described above.

In a further embodiment of the invention, a penetration member 20 withelectrodes 39, 41 or 45 on its distal end form part of a catheter thatdoes not itself comprise radial alignment electrodes. In thisembodiment, the electrodes on the penetration member 20 may be used forradial alignment prior to deployment of the penetration member 20.Alternatively, there may be no radial alignment of the catheter prior todeployment of the penetration member 20. In this embodiment, thedirection of the penetration member 20 is monitored by the signalgenerated in the sensing catheter 100 by the electric field created byelectrodes 39, 41 or 45 on the penetration member 20.

The sensing catheter 100 is shown in more detail in FIG. 4a . The hollowguide wire 106 comprises two ring electrodes 108, 110. In the embodimentshown in FIG. 1b , the most distal electrode is the sensing electrode108, whilst the proximal electrode is a grounding electrode 110. At theproximal end of the catheter 100 an electrical plug 116 (not shown) isconnected to the electrode wires 112, 114 (not shown) that run along thelength of the sensing catheter 100 within a central lumen. Each of theelectrode wires 112, 114 is in electrical connection with a respectivering electrode 108, 110. Suitably, the connector may comprise anyconnector suitable for transmitting an electrical signal, in oneembodiment, the connector is a male auxiliary plug.

FIG. 4b shows a cross section of the lumen 102 along AA as shown in FIG.4a . The electrode wires 112, 114 are shown located within the lumen 115of the body 106. In embodiments of the invention the body 106 may becomprised within a guide wire, both hollow or not, or similar catheterof small diameter.

The apparatus comprising the two catheters 10, 100 are connected to anelectronic alignment monitor system 200. The electronic alignmentmonitor system 200 applies a voltage to the distal electrodes 22, 24 ofthe source catheter 10. In one embodiment voltage is applied tospatially opposite electrodes. The voltage applied is preferably an ACvoltage. Suitably, the voltage may alternate with a frequency of between10 Hz and 1 MHz, more suitably the voltage may alternate at a frequencyof between 1 kHz and 100 kHz. Typically, the amplitude of the voltagemay be between 1 mV to 10 V. Suitably, the current has to be within thelimits set by EN60601-1. The electronic alignment system 200 may alsodisplay the alignment signal.

In one embodiment of the invention, the electronic alignment monitorsystem 200 is comprised within a hand-held unit which serves as thehandle 30 for the source catheter 10 as shown in FIGS. 5a and 5c . Thehandle 30 has a groove 43 into which the handle engagement, or rigidclip-on section 32 of the source catheter 10 clips. Pads 44 in thehandle 30 brush against the ring electrodes 34, 36 creating a 360 degreerotatable electrical connection to the source electrodes 22, 24 at thedistal end of the catheter 10 via electrode wires 26, 28. The handle 30is also in electrical communication with the sensing catheter 100.Suitably, the connection is via a female auxiliary jack plug 46 althoughany suitable means of hard-wired or wireless connection is encompassedwithin the scope of the invention. The female auxiliary jack plugconnector 46 that links the sensing catheter 100 to the handle 30 on thesource catheter 10 also functions as an on off switch for the wholesystem, turning it on when plugged in and indicating to the operatingclinician that they need to progress to the next step.

The integrated alignment system 200 within the handle 30 displaysalignment data using a visual display 48. The visual display providesfeedback to the operator of the relative positioning of the sourcecatheter 10 and the sensing catheter 100, and particularly whether thecatheters 10, 100 are correctly aligned with each other in order toundertake the creation of a fistula successfully. For example, in theembodiment shown in FIGS. 5a to c , as the source catheter is rotatedand reaches alignment the read-out successively illuminates a series ofthe LED's. In this embodiment, the LED's may also indicate otherimportant information, including, but not limited to, when the batteryis close to being discharged (flashing red), or flashing green when thesystem needs to be calibrated. Various alternative forms of userdisplays may also be contemplated for inclusion on the handle 30 or on adisplay screen or device remote from the handle. By way of non-limitingexample, displays may be visual, such as by illuminating one or a seriesof LED's, or via an LED/LCD display; aural, such as by combining twointermittent tones (beeps) until a single continuous tone is heard; orvia a sensation, whereby correct alignment is indicated to the operatorvia a vibration of the handle; or a combination of all or some of thesereadouts.

The electronic alignment monitor system 200 may be powered by any means.Suitably, the electronic alignment monitor system 200 is battery poweredand the batteries are completely integrated into the handle. The system200 generates an electrical signal that drives the source electrodes 22,24 on the source catheter 10 as well as processing the signal measuredfrom the sensing catheter 100. The system 200 is also responsible fordisplaying information to the user, for example by means of the 4 LED'sas shown in FIG. 5a . It will be understood that additional or fewerLED's may be used.

The alignment of the catheters 10, 100 for the formation of an AVF isbased on the measurement by the sensing catheter 100 of an asymmetricalelectric field generated by the source catheter 10. As shown in FIG. 6,an electric potential field measured by the sensing electrode 108 willbe greatest when the positive electrode 22 on the source catheter isperfectly aligned with the center of the sensing electrode 108. Theminimum voltage measurement will occur when the negative electrode 24 isaligned with the center of the sensing electrode 108. The sensingelectrode 108 is in the form of a ring, so its measurements areindependent of any rotation of the sensing catheter 100. In essence, thesensing electrode 108 is an omni-directional receiver of the electricalsignal (or absence of signal) generated by the source catheter 10.Therefore, if the opening 19 is in line with the positive sourceelectrode 22 it is possible to align its trajectory with the target veinthat it needs to pierce by rotating the source catheter 10 until thepeak voltage is detected by the sensing electrode 108. Alternatively theminimum or null signal can be used for alignment. In addition to theactive alignment, the electrodes themselves can act as visual indicatorsunder fluoroscopy. This provides the operating clinician with visualconfirmation that the source catheter is being rotated properly withinthe vessel. The measured voltage varies according to a sinusoidalfunction over 360 degrees with peaks occurring at 0 and 360 degrees,such as when the positive electrode 22 is aligned with the sensingcatheter 100. In one embodiment, the user is required to rotate thesource catheter 360 degrees once it is in position in order to calibratethe system. This allows the system to record the maximum amplitude inthat position. During normal use, the measured signal is comparedagainst the recorded maximum and the degree of alignment is calculated.

In a further embodiment a quadrupole arrangement of electrodes can beused. In this arrangement, when the electrodes are driven withalternating polarity the electric potential field measured by thesensing electrode 100 will vary according to a sinusoidal function over360 degrees with peaks occurring when one of the positive electrodes isaligned with the sensing catheter 100 as shown in curve Q of FIG. 6c .The connection between the electrodes and the AC voltage source can beindividually switched so that the same quadruple electrode arrangementcan be driven so that two neighbouring electrodes are connected togetherto a positive voltage, and the other two neighbouring electrodes areconnected to a negative voltage, turning the quadrupole electrodes intoa dipole arrangement. A combination of the signal obtained with thequadrupole configuration, Q(θ) and dipole configuration D(θ) can beobtained by repeatedly switching between the two configurations. FIG. 6cshows one example of a combination, where the combination:Y(θ)=D(θ)·Q(θ)+D(θ)+Q(θ) has a narrow peak at 0 degrees. This approachgives a narrower peak to increase the accuracy of the alignment.

In a further embodiment of the system a rotary encoder is used inconjunction with the dipole or multi-pole electrode configuration foralignment. This rotary encoder would be housed in the handle and measurethe angular position of the source catheter using optical, magnetic,capacitive or mechanical methods. The angular position, in conjunctionwith the measured signal strength can be used to determine the positionof the source catheter relative to the sensing catheter at any timewithout the need for calibration (for example, an initial 360 degreerotation). After even a slight rotation is it possible to determine itsexact position by inferring from the few data points the preciseamplitude curve since it is known that it is sinusoidal in shape.Therefore, angular position which corresponds to the peak amplitude canbe determined mathematically and the necessary angular rotation of thesource catheter to reach alignment can be calculated. The user is thenguided using the interface to rotate the catheter the appropriate amountand in the appropriate direction in order to reach alignment.

In a further embodiment of the system another dipole pair of electrodesis placed on the source catheter 10 in order to guide the longitudinalalignment of the catheters 10, 100. These longitudinal alignmentelectrodes 40, 42 are ring electrodes with the positive electrode (Vcc)42 placed proximal of the angular alignment electrodes 22, 24 and thenegative electrode (−Vcc) 40 placed distal of the angular alignmentelectrodes 22, 24. Both the positive and negative electrodes 40, 42 areequidistant from angular alignment electrodes 22, 24 and the separationbetween them may be between 5 mm and 10 cm. The longitudinal alignmentelectrode pair 40, 42 generates a dipole electric field in the samemanner as the angular alignment electrodes 22, 24 and the field ismeasured by the same sensing electrodes 108, 110 on the sensing catheter100. Since the field generated is centered on the angular alignmentelectrodes 22, 24, the amplitude measured by the sensing electrodes 108,110 when the angular alignment electrodes are aligned is null (FIG. 6b). During longitudinal alignment the system only activates thelongitudinal alignment electrodes 40, 42 and during rotational alignmentthe system activates only the angular alignment electrode pair 22, 24.Alternatively, the system can activate both pairs of electrodes at thesame time using different carrier frequencies or rapidly switch betweeneach electrode pair in order to get both measurements at the same time.This approach eliminates or minimizes the need for fluoroscopy to beused during the procedure.

In an embodiment of the invention, the control system 200 has four mainsub-blocks: the power unit 201, the signal generator 202, the signalprocessing unit 204, and the microcontroller unit (MCU) 206. The overallstructure is shown in FIG. 7 The power unit 201 is responsible forproviding power to the entire system. It consists of three main parts,the batteries 208, a 3 V low drop out (LDO) regulator 210 that providesVcc, and a 1.5 V LDO regulator 212 that provides the Vcc/2 rail. Thesignal generator unit 202 is responsible for generating the AC signalwhich drives the source electrodes 22, 24. A system suitable forgenerating an appropriate alternating current signal is considered to bewithin the scope of the invention. Suitably, according to embodiments ofthe invention the overall design may be based on a diode regulated Wienbridge oscillator, a clock signal from the microcontroller (MCU) or acrystal oscillator. Typically, the system comprises a diode regulatedWien bridge oscillator. The Wien bridge oscillator uses an LMV741 TexasInstruments operational (OP) amplifier which has very low noise (6.5nV/√Hz) and suitably low supply current (500 μA) and is capable ofdriving high capacitance loads. This is necessary since it is the laststage before a capacitor AC couples the output to the positive electrode22 on the source catheter 10. The signal-processing unit 204 handles theraw signal from the sensing electrode 108 in three stages and outputs aDC value to the MCU 206. The purpose of the MCU 206 is to represent thedifference in amplitude between the sensing electrode 108 and thegrounding electrode 110. The differential signal is first passed throughactive high pass filters, then an instrumentation amplifier and finallya peak detecting circuit. The microcontroller unit consists of anATTiny45 and is responsible for the analog to digital conversion andanalysis of the magnitude signal received from the signal processingunit 204. It determines the catheter alignment and displays theinformation to the user, for example, through the LED interface on thehandle 30. In alternative configurations some or all of the electroniccomponents within these sub-blocks may be replaced by suitablealternatives as known to those skilled in the art. Furthermore,additional sub-blocks may be added to improve measurement performance,signal processing, or to reduce power consumption. These additionalsub-blocks may also enable the use of any of the aforementionedadditional features (multipole electrode configurations, rotationalencoders, etc.).

In other embodiments of the invention, the alignment of the first andsecond devices may be by means other than detection of an asymmetricalelectrical field. In such embodiments a signal source, such as atransducer or transmitter, is located on the source catheter 10. Thesignal transducer provides a signal that is directed outwards from thesource catheter. Typically, the signal is directed radially outward fromthe source catheter 10 in a direction that is perpendicular to thelongitudinal axis of the source catheter 10. In alternative embodimentsof the invention the direction of the signal need not be perpendicularand can be directed at an angle of between 20° and 90°, suitably around45°, to that of the axis of the source catheter 10. The signaltransducer is, thus, comprised within a signal generating means of theapparatus of the invention.

The signal transducer is connected to a signal transmitter (not shown).The signal transmitted can be suitably selected from ultrasound orappropriate electromagnetic sources such as a laser, microwave radiationor via radio waves. In a specific embodiment of the invention the signaltransmitter generates an ultrasound signal, which is relayed to thesignal transducer, which in turn directs the signal into the surroundingtissue and which may be detected by a sensor located on the seconddevice in order to facilitate correct rotational and/or longitudinalalignment.

Methods of Using the AVF Surgical Device

The method of the invention comprises three main phases of therapy: aninsertion phase, a therapy phase and a removal phase. The insertionphase includes the intravascular insertion of the devices and thelocation of the devices to the site of treatment, in adjacent vessels,where therapy is to be administered. The therapy phase includesalignment of the devices relative to each other followed by formation ofa fistula between the respective vessels. The removal phase includes thewithdrawal of the devices from the site of treatment; usually back alongthe initial insertion route. It will be appreciated that the therapyphase may be repeated several times before the removal phase commences.

In a typical embodiment of the invention, after alignment of the devicesand formation of a conduit or fistula, the alignment system is removedleaving a guide wire in place over which a stent delivery system isdeployed. A stent is then inserted to effectively form an end to endanastomosis after which the stent delivery system is removed.

A typical clinical procedure for creating the AVF according to oneembodiment of the present invention is shown in FIGS. 8a to 8f . Theexample provided herein relates to the creation of an AVF in, or near,the wrist of a patient in need thereof. It will be appreciated that theAVF can be created in other locations within the body where relativelyadjacent vessels are located.

The first step involves inserting a guide wire 18 into the appropriateartery 302 and the sensing catheter 100 into the appropriate vein 304using any suitable technique, for example, the modified Seldingertechnique (FIG. 8a ) (see Rajan, Essentials of Percutaneous DialysisInterventions, Springer (2011)).

As best shown in FIG. 8a , the source catheter 10 is introduced over theguide wire 18 into the radial artery 302. Under suitable visualisationthe catheters 10, 100 are advanced to the appropriate longitudinalposition within the radial artery and cephalic vein. The visualisationmay be by fluoroscopy. Alternatively, phased array ultrasound may beused to visualize the longitudinal position of the catheters.

Once the source catheter 10 and the sensing catheter 100 are in place,the source catheter 10 is connected to the electronic alignment monitorsystem 200 via a cable 306 (not shown) from the sensing catheter 100 isconnected to thereto. Optionally, the source catheter handle 30 (notshown) may now indicate to the clinician that they must calibrate thesystem by rotating the catheter through 360 degrees. Next, using boththe electronic alignment monitor system 200 and fluoroscopy as a visualbackup, the clinician operator rotates the source catheter so that theopening 19, where the needle 20 exits the lumen 38 of the sourcecatheter 10, is aligned with the sensing electrode 108 (FIG. 8b ). By“aligned” it is meant that the opening 19 points in a direction towardsthe sensing electrode 108. By directing the opening 19 towards thesensing electrode 108, a known field is defined between the adjacentvessels in which the conduit or fistula may be created. It will beappreciated that without the existence of such a known field theclinician operator would effectively be working without guidance and therisk of failure is increased substantially. Once proper alignment isachieved the guide wire 18 from the source catheter 10 is removed whichreleases and allows the needle 20 to be slowly advanced by the clinicianoperator, piercing through the arterial wall, through interstitialtissue and into the adjacent cephalic vein 304 (FIG. 8c ). The directionof advancement of the needle—i.e. the needle track—is substantiallyalong the alignment plane and within the known field. Once the needle 20has crossed over successfully the clinician removes the sensing catheter100 and inserts a longer guide wire 306 into the source catheter. Thisis advanced through the hollow core of the needle 20 and further intothe vein 304 in the direction of blood flow (FIG. 8d ). Once the guidewire 306 forms a secure U shape connecting the two vessels 302, 304 thesource catheter 10 and needle 20 are retracted leaving the guide wire306 in place. A typical stent delivery catheter system 308 is thenadvanced over the guide wire 306 (FIG. 8e ). Finally, a covered stentgraft 310 is deployed, effectively forming an end to end anastomosis(FIG. 8f ). The fistula is left to mature while the vein 304arterializes, and it is monitored for potential adverse effects likehematoma, internal bleeding or steal syndrome. The fistula therebyallows the vein to act as a future vascular access point forhaemodialysis.

A further, more detailed, procedure specific to the vascular accessapplication of the invention is provided below:

As a first step the patient undergoes duplex ultrasonography todetermine if there is sufficient flow in the radial artery. An Allentest is then conducted with the aid of duplex ultrasonography todetermine that there is sufficient ulnar flow to avoid steal syndrome.

The patient is then prepared for a lower arm interventional procedure.The catheter insertion site and the anastomosis site are sterilized andlocal anaesthetic is administered. Fluoroscopy is set up to image thelower arm. Alternatively, phased array ultrasound may be used tovisualize the lower arm instead.

Next, a tourniquet is applied to the upper arm at just below thesystolic pressure in order to ensure the veins in the lower arm do notcollapse. Seldinger technique (see Rajan, Essentials of PercutaneousDialysis Interventions, Springer (2011)) is performed using amicropuncture set in order to insert a venous guide wire into thecephalic vein slightly distal to the antecubital faucet. The sensingcatheter 100 is advanced to the chosen anastomosis site which isslightly proximal to the wrist joint.

Seldinger technique is then performed using a micropuncture set in orderto deploy a guide wire 18 into the radial artery followed by theinsertion of a 7 F (0.092″, 2.3 mm) sheath over the guide wire into thebrachial artery near the antecubital faucet. The source catheter 10 isdeployed over the guide wire and advanced so that it is in line with thesensing catheter 100 based on the fluoroscopy image. In this embodimentthe guide wire is a 0.035″ (3 F, 0.95 mm) guide wire, however, it shouldbe appreciated that the guide wire may be of any suitable size

The connector cable from the sensing catheter 100 is plugged into theelectronic alignment monitor system 200, and the alignment signalmonitored while the source catheter 100 is rotated until the alignmentsignal indicates optimum alignment. The electronic alignment monitorsystem 200 may be the handle 30, in which case the connector cable fromthe sensing catheter 100 is plugged into the handle 30. In oneembodiment, the four indicator LED's will begin to blink yellow,indicating that sensing catheter 100 was connected correctly. The sourcecatheter 10 is then clipped into the handle 30. The four indicator LED'swill begin to blink green, indicating that source catheter 10 wasconnected correctly but that the apparatus needs to be calibrated.

The source catheter 10 is rotated 360 degrees by the clinician in orderto calibrate the apparatus. Any suitable means of indicating calibrationmay be used, for example, visual, audible or tactile feedback may beemployed to provide feedback to the clinician as correct calibration isachieved. In the present embodiment, all four indicator LED's will stopblinking indicating that the electronic alignment monitor system 200 hasbeen calibrated correctly.

The source catheter 10 is then rotated by the clinician in order toalign the apparatus correctly. Any suitable means of indicatingalignment may be used, for example, visual, audible or tactile feedbackmay be employed to provide feedback to the clinician of the degree ofalignment of the catheters 10,100. In the present embodiment, the fourLED's will light up one at a time a solid green. When all four LED's arelit the catheters 10, 100 are correctly aligned.

The clinician may then retract the guide wire 18 until a marker band isvisible at the proximal end of the catheter 10 and the guide wire 18 isthen locked into place. This indicates that the penetration member 20can now be deployed. A syringe is attached to the proximal end of thepenetration member 20. The penetration member 20 is then advanced by theclinician under fluoroscopy guidance to puncture out of the artery andinto the cephalic vein. Flashback blood is collected into the syringeindicating that a successful puncture was made.

The guide wire 18 is advanced again through the penetration member 20until it is sufficiently deployed within the vein in the progradedirection. The source catheter 10 and sensing catheter 100 are removedcompletely leaving only the guide wire 18 in place which crosses fromartery to vein.

A 6 F stent graft delivery system may then be deployed over the guidewire that is left in place. The stent graft is advanced over the guidewire into the vein and is then deployed according to the manufacturers'instructions in order to create the AVF.

In an embodiment of the method, contrast medium is delivered to ensurethere are no leaks. The tourniquet may then be removed. The deliverycatheter may then also be removed followed by the removal of theintroducer sheath. Pressure is then applied at the entry sites into theartery and the vein. Bandages are applied and the patient is prepped toleave the operating room.

Several anatomical sites are suitable for the creation of the fistula.Ultrasound studies indicate that sites such as the brachial artery andmedian cubital vein, the brachial artery and the cephalic vein, as wellas the radial artery and cephalic vein are suitable locations for thecurrent invention to be used in. In the specific embodiment of thisinvention, the radial artery and cephalic vein are to be used forcreating a fistula.

In another application the source catheter 10 and the sensing catheter100 are inserted into a coronary artery and vein using interventionaltechniques.

Using standard femoral access a standard guide catheter is inserted fromthe femoral artery, through the aorta to the coronary ostium. A guidewire is inserted into the coronary artery under fluoroscopic guidance.The source catheter 10 is deployed over the guide wire and advanced sothat it is in line with the sensing catheter 100 based on thefluoroscopy image.

The sensing catheter 10 is inserted into the coronary vein by anysuitable route, for example from the femoral vein, via the iliac veinsto the inferior vena cava to the right atrium and via the coronary sinusto the coronary vein.

In this embodiment, the calibration of the apparatus and alignment ofthe catheters is generally as for the venous access application above.

Once alignment is optimized, as determined by the electronic alignmentmonitor system 200, the clinician retracts the guide wire 18 until amarker band is visible at the proximal end of the catheter 10 and theguide wire 18 is then locked into place. This indicates that thepenetration member 20 can now be deployed. The penetration member 20 isthen advanced by the clinician under fluoroscopy guidance to punctureout of the coronary artery and into the neighbouring coronary vein.

The guide wire 18 is advanced again through the penetration member 20until it is sufficiently deployed within the vein. The source catheter10 and sensing catheter 100 are removed completely leaving only theguide wire 18 in place which crosses from the artery to the vein.

A stent graft delivery system is deployed over the guide wire that isleft in place. The stent graft is advanced over the guide wire into thevein and is then deployed according to the manufacturers' instructionsin order to create an arteriovenous anastomosis between artery and veinin order to divert oxygenated blood to the vein.

In another embodiment of the invention, the source catheter is insertedinto the popliteal artery or the tibial artery and the sensing catheteris inserted into the posterior tibial vein, in order to deliver anS-shaped graft from the artery to the vein that diverts blood to thelower limb extremities to treat critical limb ischaemia.

In this application, the calibration of the apparatus and alignment ofthe catheters is generally as for the venous access applicationdescribed in more detail above.

Once alignment of the devices is optimized between poplitealartery/tibial artery and the posterior tibial vein, as determined by theelectronic alignment monitor system 200, the clinician retracts theguide wire 18 until a marker band is visible at the proximal end of thecatheter 10 and the guide wire 18 is then locked into place. Thisindicates that the penetration member 20 can now be deployed. Thepenetration member 20 is then advanced by the clinician underfluoroscopy guidance to puncture out of the artery and into the adjacentvein.

Where the penetration member comprises a hollow needle, a guide wire 18is advanced again through the penetration member 20 until it issufficiently deployed within the vein. The source catheter 10 andsensing catheter 100 are removed completely leaving only the guide wire18 in place which crosses from the artery to the vein through theintervening tissue.

A stent graft delivery system is deployed over the guide wire that isleft in place. The stent graft is advanced over the guide wire into thevein and is then deployed according to the manufacturers' instructionsin order to create an arteriovenous anastomosis between artery and veinin order to divert oxygenated blood to the vein.

In yet another embodiment the methods and devices of the invention canbe used in a Blalock-Taussig procedure in order to increase pulmonaryblood flow for palliation in duct-dependent cyanotic heart defects suchas pulmonary atresia. In this embodiment, the source catheter may beinserted into one branch of the subclavian artery or carotid artery andthe sensor catheter is connected to the pulmonary artery. According tothis embodiment the calibration of the apparatus and alignment of thecatheters is generally as for the venous access application described inmore detail above. The guide wire 18 may be advanced again through thepenetration member 20 until it is sufficiently deployed within thetarget vessel. The source catheter 10 and sensing catheter 100 areremoved completely leaving only the guide wire 18 in place which crossesfrom one vessel to the other. A Blalock-Taussig shunt is then deployedover the guide wire that is left in place between the two vessels andthe guidewire withdrawn to leave the stable connection between the twovessels.

In another embodiment, a short 4 F (1.135 mm) introducer sheath may beplaced into the left or right common femoral artery with a modifiedSeldinger technique and the source catheter is inserted through thesheath into the external iliac artery. An 11 F (11.52 mm) customisedvenous introducer is placed in the ipsilateral common femoral veinapproximately 2 cm inferior to the arterial sheath insertion site andthe sensor catheter is inserted into the distal external iliac vein. Thesource catheter 10 is then rotated by the clinician in order to alignthe apparatus of the invention correctly, as described in more detailabove. The penetration member 20 is then advanced by the clinician,optionally under fluoroscopy or ultrasound guidance, to puncture out ofthe artery and into the cephalic vein. The guide wire 18 is advancedagain through the penetration member 20 until it is sufficientlydeployed within the vein. The source catheter 10 and sensing catheter100 are removed completely leaving only the guide wire 18 in place whichcrosses from one vessel to the other.

A coupler or graft such as the ROX Coupler (ROX Medical, San Clemente,Calif., USA) is placed between the artery and the vein in the pelvicarea to create an anastomosis—a passage through which blood can flow.This anastomosis, or passage, reduces the peripheral vascular resistanceand may lower arterial blood pressure in hypertensive patients.

In another embodiment of the invention, the source catheter 10 may beinserted into the sub-intimal space of an artery with a total occlusion,the insertion is over an existing guide wire that has been previouslyinserted into the space. The sensing catheter 100 is inserted into thesame artery from a site distal to the occlusion. The source catheter 10is advanced past the occlusion, and is rotated by the clinician in orderto align the apparatus correctly towards the sensing catheter and thusback into the true lumen of the artery. In a variant of the method forthis application the sensing catheter 100 is inserted into a vein thatruns parallel to the artery. The source catheter 10 is inserted past theocclusion, and is rotated by the clinician in order to align theapparatus correctly towards the sensing catheter. The source catheter isrotated by 180° so the alignment signal indicates the source catheter isfacing away from the vein, and thus back into the true lumen of theartery. In both variants of the method the penetration member 20 is thenadvanced by the clinician, optionally under fluoroscopy or ultrasoundguidance, to puncture out of the subintimal space and into the truelumen of the artery. The guide wire 18 is advanced again through thepenetration member 20 to re-enter the artery. The source catheter 10 andsensing catheter 100 are removed completely leaving only the guide wire18 in place which crosses from one chamber to the other. An angioplastyballoon and stent can then be deployed over the guide wire to form ablood channel through the sub-intimal space around the occlusion.

It will be appreciated that in another embodiment of the invention thesystem and apparatus may be utilised for general laparascopicprocedures. In this embodiment, the source catheter 10 and the sensingcatheter 100 are inserted into neighbouring vessels, chambers,ventricles or cavities via a percutaneous vascular route or though atrochar using standard laparascopic techniques.

In this embodiment, the calibration of the apparatus and alignment ofthe catheters is generally as for the venous access applicationdescribed in more detail above.

Once alignment is optimized, as determined by the output of theelectronic alignment monitor system 200, the penetration member 20 isthen advanced by the clinician under fluoroscopy guidance to punctureout of one chamber and into the neighbouring chamber.

The guide wire 18 is advanced again through the penetration member 20until it is sufficiently deployed within the target chamber. The sourcecatheter 10 and sensing catheter 100 are removed completely leaving onlythe guide wire 18 in place which crosses from one chamber to the other.The guide wire can then be used to guide the deployment of a catheterwhich can be used to install, for example, a trans-chamber device, suchas a stent graft, a valve, an intra-septal device or a pressure sensor.

Although particular embodiments of the invention have been disclosedherein in detail, this has been done by way of example and for thepurposes of illustration only. The aforementioned embodiments are notintended to be limiting with respect to the scope of the appendedclaims, which follow. It is contemplated by the inventors that varioussubstitutions, alterations, and modifications may be made to theinvention without departing from the spirit and scope of the inventionas defined by the claims.

REFERENCES

J. J. P. M. Leermakers, A. S. Bode, A. Vaidya, F. M. van der Sande, S.M. A. A. Evers, and J. H. M. Tordoir, “Cost-effectiveness of VascularAccess for Haemodialysis: Arteriovenous Fistulas Versus ArteriovenousGrafts,” European Journal of Vascular & Endovascular Surgery, vol. 45,no. 1, pp. 84-92, January 2013.

-   Department of Health and Human Services, Health Resources and    Services Administration, Healthcare Systems Bureau, Division of    Transplantation, “2014 Annual Report of the U.S. Organ Procurement    and Transplantation Network and the Scientific Registry of    Transplant Recipients,” University Renal Research and Education    Association, Ann Arbor, 2014.-   A. A. Al-Jaishi, Oliver, S. M. Thomas, C. E. Lok, A. X. G. M., S. D.    K., R. R. Q, and L. M. M., “Patency Rates of the Arteriovenous    Fistula for Hemodialysis: A Systematic Review and Meta-analysis,”    YAJKD, vol. 63, no. 3, pp. 464-478, March 2014.-   Rajan, Essentials of Percutaneous Dialysis Interventions, 2011,    Springer-   Dimitris C L 2008 Shape Memory Alloys: Modelling and Engineering    Applications (Berlin: Springer)-   Melvin D Lobo et. Al. ‘Central arteriovenous anastomosis for the    treatment of patients with uncontrolled hypertension (the ROX    CONTROL HTN study): a randomised controlled trial’ The Lancet Volume    385, No. 9978, p 1634-1641, 25 Apr. 2015

What is claimed is:
 1. A method for improving venous access in a patientin need thereof by creating a fistula between a first vessel and asecond vessel, the method comprising the steps of: a) inserting, via apercutaneous route, a first device into the first vessel, wherein thefirst device comprises a catheter that comprises a directional signalsource, and wherein the first device further comprises a penetratingelement that is capable of being advanced radially outwardly from thefirst device, the direction of advancement of the penetrating elementbeing aligned to a directional signal produced by the directional signalsource; b) inserting, via a percutaneous route, a second device into thesecond vessel, wherein the second device comprises a sensor, wherein thesensor is capable of detecting a directional signal; c) generating adirectional signal and aligning the first and second devices relative toeach other such that penetrating element is advanced radially from thefirst vessel towards the second vessel, thereby forming a channelenabling fluid communication between the first and second vessels; andd) enlarging the channel to form a fistula.
 2. The method of claim 1,wherein the first vessel is an artery and the second vessel is a vein.3. The method of claim 1, wherein the first vessel is a vein and thesecond vessel is an artery.
 4. The method of claim 1, wherein thefistula is an arterio-venous fistula (AVF).
 5. The method of claim 1,wherein the first and second vessels are located in a limb of the body.6. The method of claim 5, wherein limb is an arm.
 7. The method of claim5, wherein the limb is a leg.
 8. The method of claim 1, wherein themethod is for facilitating haemodialysis.
 9. The method of claim 1,wherein the first device is inserted over a guidewire.
 10. The method ofclaim 1, wherein the second device comprises a catheter and is insertedover a guidewire.
 11. The method of claim 1, wherein the second devicecomprises a guidewire.
 12. The method of claim 1, wherein penetratingmember comprises a needle.
 13. The method of claim 12, wherein theneedle is hollow.
 14. The method of claim 12, wherein needle comprises amaterial selected from the group consisting of: a polymer; a shapememory alloy; stainless steel; and titanium.
 15. The method of claim 14,wherein the shape memory alloy is Nitinol™.
 16. The method of claim 1,wherein penetrating member comprises a flexible guidewire.
 17. Themethod of claim 1, wherein aligning the first and second devicesrelative to each other occurs via the detection of a peak signal by thedirectional signal source by the signal sensor.
 18. The method of claim1, wherein the directional signal source comprises at least oneelectrode.
 19. The method of claim 18, wherein the at least oneelectrode generates an asymmetrical electric field.
 20. The method ofclaim 1, wherein the directional signal source comprises a plurality ofelectrodes.
 21. The method of claim 20, wherein the plurality ofelectrodes generates an asymmetrical electric field.
 22. The method ofclaim 1, wherein the directional signal source comprises at least onesignal transmitter.
 23. The method of claim 22, wherein the signaltransmitter generates a directional electromagnetic signal.
 24. Themethod of claim 22, wherein the signal transmitter generates adirectional ultrasound signal.
 25. The method of claim 1, wherein thedirectional signal enables rotational alignment of the first and seconddevices relative to each other.
 26. The method of claim 1, wherein thedirectional signal enables longitudinal alignment of the first andsecond devices relative to each other.
 27. The method of claim 1,wherein the directional signal enables rotational and longitudinalalignment of the first and second devices relative to each other. 28.The method of claim 1, wherein enlargement of the channel is via astent.
 29. The method of claim 28, wherein the stent comprises aself-expanding stent
 30. A method of connecting two adjacent vesselswithin the body of a patient, said method comprising the steps of: a)introducing a first source device into a first vessel, the first devicecomprising at least one signal electrode for generating an asymmetricelectric field; b) introducing a second sensing device into a secondvessel, the second device comprising at least one detector for detectingthe asymmetric electric field; c) aligning the first and second devicerelative to each other based on the electric field generated by thefirst device that is detected by the detector on the second device; d)forming a conduit between the first vessel and the second vessel; and e)removing the first and second devices to leave the first and secondvessels connected via the conduit.
 31. The method of claim 30, whereinthe first device comprises a catheter.
 32. The method of claim 30,wherein the second device comprises a catheter.
 33. The method of claim30, wherein the alignment of the first and second device is determinedby the amplitude of the asymmetric electric field as detected by thedetector on the second device.
 34. The method of claim 33, wherein theoptimal alignment of the first and second device is at a maxima orminima of the amplitude of the electric field detected by the detectoron the second device.
 35. The method of claim 30, further comprising anadditional step between step (b) and step (c) of calibrating the firstand second devices.
 36. The method of claim 35, wherein the calibrationcomprises rotating the first device between 0 to 360° with respect tothe second device.
 37. The method of claim 30, wherein the conduitbetween the first vessel and the second vessel is formed by apenetrating member.
 38. The method of claim 37, wherein the penetratingmember comprises a needle.
 39. The method of claim 38, wherein theneedle is retained within the first device prior to deployment to formthe conduit.
 40. The method of claim 38, wherein the needle is retainedwithin the second device prior to deployment to form the conduit. 41.The method of claim 39, wherein the conduit between the first vessel andthe second vessel is formed by advancing the needle in a radialdirection outwardly from the first device.
 42. The method of claim 40,wherein the conduit between the first vessel and the second vessel isformed by advancing the needle in a radial direction outwardly from thesecond device.
 43. The method of claim 42, wherein the advancement ofthe needle is guided by a monitoring system external to the body of thepatient.
 44. The method of claim 43, wherein the monitoring system isselected from fluoroscopy and phased array ultrasound.
 45. The method ofclaim 30, further comprising installing a trans-vessel device in orderto stabilise the conduit, wherein between steps (d) and (e) a guide wireis advanced through the conduit, the guide wire being left in place whenthe first and second device are removed, and following step (e) atrans-vessel device is installed over the guide wire.
 46. The method ofclaim 45, wherein the trans-vessel device comprises a stent.